In the microelectronics industry, the requirements for increased circuitry for a given chip size has driven to smaller half-pitch nodes in order to increase the process speed and improve the chip efficiency. Microlithography techniques are key to reducing the size of structural features. The depth of focus and resolution depend on the numerical aperture of the lithography apparatus and the wavelength of light.
Double Patterning is a class of technologies developed for photolithography to enhance the feature density. For the semiconductor industry, double patterning may be the only lithography technique to be used for the 32 nm and 22 nm half-pitch nodes using the 193 nm immersion lithograph tools available today. There are four common schemes available to double patterning: (1) double exposure; (2) self-aligned spacer mask; (3) heterogeneous mask; and (4) immediate pattern accumulation. Among these, self-aligned spacer mask is probably the most promising technology however, the process is very sophisticated and involves many complex steps. Typically a spacer material is firstly formed on the sidewall of a pre-patterned feature, applied either by a spin-on or deposition process, followed by etching to remove all the film material on the horizontal surface, leaving only the sidewalls. After removing the original patterned feature, only the spacer is left. Since there are two spacers for every line, the line density is doubled.
In order for a silicon containing material to be useful in double patterning, it must meet several criteria. First it must be in a solvent that the photo-resist is not soluble in such as an organic alcohol or ether. Additionally, it must be capable of being cured by multiple cure methods to allow for the formation of select compositions that can be etched by different etch methods such as CF4 and O2. It has been found that certain silsesquioxane resins meet these criteria.